Frottage & STIs among gay

Asked for Male, 26 Years

I have read a lot about frottage and they consider it safe for HIV and Hepatitis. But I am still unsure of this in some scenarios. In a situation where two men are rubbing their penis on each other's penis and surrounding area, and if the there are visible abrasions (mild to deep) or cuts are present before, during or after the act on both or any of the person (either on penis or glans penis, whether circumsized or not, because of rubbing, or on the senstive skin between testicles and inner thigh because of excessive sweating in general or by the process of rubbing itself), and they have precum dripping also, what are the chances of getting STIs, especially HIV and hepatitis, if the abraded skin is exposed by precum. What in the case if they ejaculate and the the abraded skin come in contact with semen?